The present invention relates to a tactile switch used in a portable telephone, portable radio receiver, camera and others.
FIG. 6 is a plan view showing a conventional tactile switch, FIG. 7 is a sectional view taken along a line VIIxe2x80x94VII of FIG. 6, FIG. 8 is a bottom view of the tactile switch and FIG. 9 is a plan view showing a substrate 1.
The tactile switch has a side of 4 mm and a thickness of 0.5 mm. The switch has a substrate 1, a first fixed contact 5 secured to the substrate 1, a spring contact 4 mounted on the first fixed contact 5 and a flexible cover 3 made of plastic and secured to the substrate 1 through a spacer 2 so as to provide a watertight sealing.
The spring contact 4 has a semispherical shape and is surrounded by a wall of a circular hole 2a of the spacer 2. Each of four corners of the substrate has a semicircular recess. As shown in FIG. 8, four terminal electrodes 9a to 9d are secured to the underside of the substrate 1 at the four corners in order to connect the tactile switch with an instrument to be mounted therein. Each of the terminal electrodes 9a to 9d is connected to a conductive pattern on the substrate 1 through a lead provided on the semicircular recess.
As shown in FIGS. 7 and 9, the first fixed contact 5 is provided on a peripheral portion of the substrate to form a circular vacancy, and connected to the terminal electrode 9a through the lead on the semicircular recess. The spring contact 4 is contacted with the first fixed contact 5 at the peripheral edge thereof.
A second fixed contact 6 is securely mounted on the underside of the substrate 1 at a central portion of the circular vacancy. The second fixed contact 6 is connected to the terminal electrode 9c by a lead provided in a through-hole 7 and a conductive pattern 8.
The spring contact 4 is depressed through the cover 3 by a push button provided in the instrument, so that a central portion of the spring contact 4 is downwardly bent. When the spring contact 4 passes a neutral point, the spring contact quickly inverts. Thus, the spring contact contacts with the second fixed contact 6, so that the first fixed contact 5 is connected to the second fixed contact 6.
Such a tactile switch must endure a large number of operations. For example, the tactile switch mounted in the portable telephone must endure over 500,000 operations. For the long life, stainless steel is used for the spring contact. However, the stiffness of the spring contact is liable to be extremely high, because the size of the spring contact is very small. As a result, the spring contact strikes hard against the second fixed contact, thereby producing harsh noises.
In addition, the through-hole 7 causes the manufacturing cost of the tactile switch to increase.
An object of the present invention is to provide a tactile switch which is simple in construction, excellent in function, and has a long life and high reliability.
According to the present invention, there is provided a tactile switch comprising a substrate, an annular first fixed contact provided on the substrate, a second fixed contact provided on the substrate within the first fixed contact, a spherical spring contact having legs contacted with the first fixed contact.
Each of the legs contacts with the first fixed contact at a peripheral edge thereof.
An arc portion is formed between adjacent legs.
The second fixed contact is connected to a terminal electrode by a conductive pattern passing through a passage formed in the first fixed contact and a space formed under the arc portion.
These and other objects and features of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.